Thanks all for the info...
I have been experimenting with a codex called speex (www.speex.org) and can
get decent results down to about 5kbps, just after the first night. I am
sure I can get it down less than that.
There is a LOT of header overhead with AX.25 and that is something that will
have to be death with for my little project. I was hoping to overcome this
problem by going to very high speeds. I just purchased a Kantronics TNC,
supposedly capable of up to 32kbps and even 56kbps with a little circuit
change.
I have been looking around for some alternate protocol that gives a larger
data segment. Any suggestions???
73s
Ken KC7RAD
----- Original Message -----
From: "Nicolai Heilemann"
<nicolai_oliver.heilemann at student.fh-reutlingen.de>
To: "TAPR Digital Voice Mailing List" <digi-voice at lists.tapr.org>
Sent: Wednesday, October 27, 2004 11:51 PM
Subject: Re: [digi-voice] Digital voice over high-speed packet
>> I have done some LPC tests on a 9k6 channel using RAT (Robust Audio Tool
> by the University College of London) with focus on speech quality
> assessment. The result where not too uplifting. (Or lets face it: I proved
> that it works in principle, but don't expect more ;) ).
>> In general a 9k6 channel is able to transport speech if you compress it
> down to 2kBit or so, (not more as with AX.25 you have an awfull lot of
> packet header overhead), but as you can expect with such a high
> compression the speech is extremely vulnerable to packet losses (which
> will occur quite often as you cannot use balanced mode but have to send
> everything as UI frames as you would end up with no real time any more
> otherwise), so it simply sounds quite poor.
>> Anyway it would be interesting to use more sophisticated codecs (CELP or
> MELP-based or so) which deliver a higher speech quality by themselves than
> LPC and see whether this would lead to satisfying results.
>> If you are interested in some detailed results, I am happy to share, and I
> also would be awfully interested in the outcome of your experiments of
> course.
>> Vy 73 es 55 de
>> Nicolai, DL9TS
>>> At 01:09 AM 28/10/2004, you wrote:
>>>>> Hi all,
>>>>>> Is there anyone on the list that knows whether anyone is doing anything
>>> with digital audio over packet? Any info would be appreciated.
>>>>>> I have heard of the occasional station using Speak Freely running LPC-10
>> over 9600 bps packet with reasonable results (on a clear channel).
>>>> 73 de VK3JED
>>http://vkradio.com>>>>------------------------------------------------------------------------
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